Electrostatic discharge (ESD) is a problem in the utilization, manufacturing and/or design of the semiconductor devices. The integrated circuits manufactured on the semiconductor device can be damaged when ESD events are received from other circuits coupled to the semiconductor device or from people and/or machinery and tools touching the semiconductor device. During an ESD event the integrated circuit may receive a charge which leads to relatively large voltages during a relatively short period of time. If, for example, the integrated circuit breaks down as the result of the high voltage and starts to conduct the charge of the ESD event, a current of several amperes may flow through the integrated circuit during a relatively short period of time. These currents may cause irreparable damage to the integrated circuit.
Today most integrated circuits comprise ESD protection circuitries that are able to conduct the charge of an ESD event to, for example, the ground without causing irreparable damage to the integrated circuit. Such ESD protection circuits are typically arranged near the I/O pads of the semiconductor device and are configured to conduct the charge of the ESD event directly to the ground before the current may reach the vulnerable portions of the integrated circuit.
In published article “New High Voltage ESD Protection Devices Based on Bipolar Transistors for Automotive Applications”, Gendron A. et al, 33th Electrical Overstress/Electrostatic Discharge Symposium, 11-16 Sep. 2011, a cross-sectional view of the structure of an ESD protection device as presented in FIG. 1a and FIG. 2a are usable ESD protection devices for automotive applications. The presented structure and circuit is especially well capable of protecting integrated circuits which are classified as “high voltage circuits”, which means in practical cases that such integrated circuits switch voltages which are higher than 5 Volts.
If the I/O pad of the semiconductor device 100 receives an ESD event of a positive voltage, the semiconductor device forms the indicated circuit of transistors T1 and T2 as presented in FIG. 1a and FIG. 1b. The circuit of transistors T1 and T2 form a thrysistor-like circuit, also often indicated with the term Silicon Controlled Rectifier (SCR). As soon as the voltage across the reverse biased N-P junction from the central N-doped region towards the P-doped region 102 becomes higher than the breakdown voltage of this junction, an avalanche phenomenon by impact ionization is created. A hole current flows through from the p-doped region 102. The p-doped region is resistive and once the voltage difference between the N-doped region (which is connected to ground) and the p-doped region 102 becomes larger than 0.3 volt, transistor T2 starts to operate, and, thus, the presented SCR starts to conduct a current from the I/O pad towards the negative or ground voltage. Thus, the breakdown voltage of the discussed junction is the trigger voltage of the ESD protection device. The start of the operation of the SCR causes the reduction of the voltage across the ESD protection device. This reduction of the voltage is termed ‘the snapback behaviour’ of the ESD protection device. If, subsequently, the current through the ESD protection device increases, the voltage across the ESD protection device also increases until a complete breakdown of the structure. In FIG. 1c the typical behaviour of such an ESD protection device is presented. As shown in FIG. 1c, if the voltage of the ESD event raises to the trigger voltage Vt the operation of the SCR starts and the voltage drops towards the holding voltage Vh. The difference between the trigger voltage Vt and the holding voltage Vh is called the snapback voltage Vsb. Subsequently, the ESD protection device is capable of conducting larger currents until the ESD protection device breaks down at point 162.
In many applications, a strong snapback behaviour is not desired and, in other application, even no snapback behaviour is allowed. Consequently, the ESD protection device of the cited patent application can not be used in such applications.